﻿Oreocharisphuongii (Gesneriaceae), a new species from central Vietnam

﻿Abstract Oreocharisphuongii, a new species of Gesneriaceae from central Vietnam, is described and illustrated here. The new species is most similar to O.longifolia by sharing peduncles up to 22 cm long, bracts 2, zygomorphic, yellow flowers with tubular corolla, stamens 4 with two pairs of coherent anthers and capsules up to 6 cm long. It mainly differs from the latter by the combination of some morphological characters of leaves (shape, base, apex and margin), size of calyx lobes, indumentum of corolla tube and inner surface of three lower corolla lobes. Detailed morphological description together with colour illustration, information on phenology, distribution, ecology, preliminarily conservation status of the new species and comparison with its similar species are also presented.


Introduction
The genus Oreocharis Bentham (Gesneriaceae DC), prior to recent phylogenetic work, comprised ca. 28 species, mainly distributed in southern China (Li and Wang 2004). Recent molecular and morphology-based analyses demonstrated that the traditionally-defined Oreocharis was phylogenetically intertwined with nine previously defined small genera and acaulescent, rosette forming members of Briggsia Craib. The re-circumscribed Oreocharis is a strongly supported monophyletic group and placed in the subfamily Didymocarpoideae (Möller et al. 2011;Middleton et al. 2013). Since its re-definition in 2011, Oreocharis s.l. comprises about 150 species making the genus one of the most morphologically diverse amongst Old World Gesneriaceae Möller 2019;Jin et al. 2021). Most of the approximately 130 species are found in southern and south-western China, with a few species also in northern Vietnam, India, Bhutan, Myanmar, Thailand and Japan (e.g. Pham 2000;Vu 2005Vu , 2018Wei et al. 2010;Möller et al. 2011Möller et al. , 2016Möller et al. , 2018Do et al. 2017;Chen et al. 2017Chen et al. , 2018Yang et al. 2019;Cai et al. 2019;Jin et al. 2021).
Prior to this work, eight species of Oreocharis were known from Vietnam, of which seven new species were described from the country since 2017, i.e. O. caobangensis T.V.Do, Y.G. Wei & F.Wen (Do et al. 2017  . All these species have been found in close proximity or with sympatric distributions in northern Vietnam, but none of them has been recorded from the central and southern areas of the country. Due to similarities of topography and ecological factors, the flora of northern Vietnam is similar to that of south-western and southern China, which is considered the centre of Oreocharis diversity (Jin et al. 2021). Additionally, there are still many parts of northern and central Vietnam (such as the Annamite Range) from which specimens of vascular plants, in general and Gesneriaceae, in particular, have not yet been well collected or for which the collecting density is very low. Hence, our understanding of the diversity and distribution of vascular plant species, in general and Gesneriaceae species, in particular, in these regions remains rudimentary.
While revising the taxonomy of Gesneriaceae for the Flora of Vietnam, we have conducted numerous field investigations throughout the country and collected some interesting Gesneriaceae specimens from two populations in some protected forest areas within the Annamite Range in central Vietnam. These specimens are characterised by leaves in a basal rosette, 2-paired stamens, ring-like disc and loculicidal capsules. Due to the above characteristics, we determined that these specimens belong to Oreocharis s.l. Detailed morphological comparisons with the protologues and type specimens of all previously-described species of Oreocharis s.l. (Pan 1987;Wang et al. 1990Wang et al. , 1998Li and Wang 2004;Wei et al. 2010;Liu et al. 2012;Chen et al. 2013Chen et al. , 2014Chen et al. , 2015Chen et al. , 2016Chen et al. , 2017Chen et al. , 2018Tan et al. 2013Tan et al. , 2015Möller et al. 2014Möller et al. , 2018Möller 2015;Li and Li 2015;Yang et al. 2015aYang et al. , 2015bYang et al. , 2017Yang et al. , 2019Wei et al. 2016;Li et al. 2017;Do et al. 2017;Cai et al. 2019 revealed that these specimens do not match with any known Oreocharis species. Therefore, we confirmed that these specimens represent a new species, which is here described and illustrated, namely O. phuongii T.V.Do. Diagnosis. The new species is morphologically similar to O. longifolia W.H.Chen in having peduncles up to 22 cm long, bracts 2, zygomorphic, yellow flowers with tubular corolla, stamens 4 and capsules up to 6 cm long; but it differs from the latter in its elliptic to ovate lamina (vs. narrowly elliptic to oblanceolate), cuneate to nearly rounded leaf base (vs. attenuate), obtuse to almost rounded leaf apex (vs. acute), crenulate margin (vs. serrulate), 3-4.5 × 1.5-1.8 mm calyx lobe size (vs. 5-7 × 2-3 mm), glabrous inner surface of corolla tube (vs. sparsely glandular puberulent with darkpurple striations) and exclusively yellow inner surface of three lower lobes without dots and striations (vs. brown to brownish-yellow with purple dots and striations).
Etymology. The specific epithet honours Prof. Dr. Vu Xuan Phuong who has contributed significantly to our understanding of Gesneriaceae in Vietnam.

Phenology. Flowering was observed from October to November. Fruiting may occur from November to December.
Distribution and habitat. The new species is currently known from some protected forest areas (viz. Dakrong Nature Reserve, Quang Tri Province and Bach Ma National Park, Thua Thien Hue Province) within the Annamite Range, central Vietnam (Fig. 3). The new species grows on moist shady cliffs on the humus-rich limestone hills and moist rocks under evergreen broad-leaved forests, at elevations of 360-650 m.
Proposed IUCN conservation status. Two large-sized populations of Oreocharis phuongii were found in the core-zones of Dakrong Nature Reserve, Quang Tri Province and Bach Ma National Park, Thua Thien Hue Province, central Vietnam, which are almost entirely covered by primary forest and are well protected. Furthermore, our field observations of these populations indicated that there are many healthy individuals and seedlings that regenerate in well-protected habitats and there is no immediate threat to the populations from human activities. Thus, the new species is probably not at risk in the near future. This species is preliminarily assessed as Least Concern (LC) according to the IUCN Categories and Criteria (IUCN Standards and Petitions Subcommittee 2019).
Notes. In the size and shape of the corolla and the structure of inflorescences, O. phuongii is similar to some species with the acaulescent and rosette-forming stems of the formerly circumscribed Briggsia, which previously comprised ca. 30 species and four varieties and was mainly distributed in Bhutan, China, India, Myanmar and Vietnam (Wang et al. 1990(Wang et al. , 1998Vu 2018). Nineteen species and four varieties of acaulescent, rosette forming Briggsia (Craib 1920;Pan 1988) were moved to Oreocharis s.l. in a later revision (Möller et al. 2011. Of which, O. phuongii is most similar to O. longifolia (Craib) Mich.Möller & A.Weber in having peduncles up to 22 cm long, bracts 2, zygomorphic, yellow flowers with tubular corolla, stamen 4 with two pairs of coherent anthers and capsules up to 6 cm long, but it clearly differs from the latter in the shape of leaf blade, leaf base, leaf apex, leaf margin, number of flowers, shape and size of calyx lobes, inner surface of corolla tube and inner surface of three lower corolla lobes. Detailed morphological comparisons of the new species with O. longifolia are shown in Table 1 and Figure 2.
This new species is the first record of the genus Oreocharis occurring in central Vietnam, which raised the species number of Oreocharis in Vietnam to nine. Amongst the nine known Oreocharis species from Vietnam, the new species shares the yellow to orange corolla with five other species: O. aurea, O. argyrophylla, O. grandiflora, O. longituba andO. tribracteata (Chen et al. 2017, 2018;Möller et al. 2018). However, it is clearly different from these five species by having a tubular corolla tube (vs. funnel to narrowly funnel corolla tube in O. argyrophylla, O. grandiflora, O. longituba, O. tribracteata and urceolate corolla tube in O. aurea). Jin et al. (2021) showed that Oreocharis sl. could be separated into two clades: Clade A was mainly distributed in SW China and predominantly showed yellow to orange corollas; Clade B was mainly distributed in S and SE China and predominantly showed purple corollas, of which, Clade A includes ca. 20 species. In order to facilitate identification, a key to five yellow to orange species of Oreocharis in Vietnam is provided.
A key to yellow to orange species of Oreocharis in Vietnam  Wang et al. (1998) and our own observations.